RF Modules (Zigbee)

[Normnet]

These use a self healing mesh networking topology so you can introduce as many nodes as you wish to your network and once created by you the network manages itself.

Is the mesh in hardware or is it code with a C or Basic example?

Norm

[Chris Barron]

Is the mesh in hardware or is it code with a C or Basic example?

Norm

Norm,
these particular modules are based on the Ember EM250 chips, which have the Zigbee stack built in, written in C code.

you could, if yoiu wanted, blow away all signs of the Zigbeee software and use the devices as ordinary IEEE 802.15.4 compatible radio modules, IE just use the hardware and lay your own software on top. Ember provide the required development tools to do that, as do (I think) Telegesis, who will help you out with any special versions of firmware you might require.

Once I started to play I realised that it might be fun to try to implement something similar in PicBasic for use with the vanilla 433MHz (etc) modules. The software stack needn't be too large. Microchip offer two stacks for their hardware, one if them is Zigbee 2006, the other is their own protocol called 'MiWi', which is a 'star and cluster' topology capable of sending messages between nodes which are a couple of hops away from each other.
The Microchip stacks are written in C and are free to download from the Microchip website, and may provide some ideas. MiWi is a significantly smaller protocol than Zigbee, and can be implemented in a smaller pic than is required for Zigbee

Chris

[Chris Barron]

I've just been reading an online newsletter (Free to subscribe to if anyone wants to stay up to date)
http://www.embedded.com/217400339?cid=NL_embedded
....which poiints out that the Zigbee Alliance is planning further integration of internet standards into the Zigbee protocol. This would mean that you ought to be able to connect anything to the internet using wireless (plus a gateway too, of course)

[Ioannis]

Nice one. Thanks Chris.

Ioannis

[lester]

If your building a ZIGBEE or any other wireless network at 2.4ghz, a major consideration is through put of data and integrity of the wireless link.

Its a good idea to use a spectrum analyser to ensure that your locality is clear of potential killer interferance such as baby monitoring devices, leaky microwave ovens, wire less video camera's and wireless alarm modules, all of which can cripple zigbee or 802.11 network performance

Take a look at www.wi-spy.co.uk

Here is a little video that explains the project range

for home users there is a low cost option: http://www.crownhill.co.uk/product.php?prod=2139

Seriously worth the money, even we cleared up a rougue 2.4ghz signal radiating intermittantly accross the band, without wi-spy we'd probably never have found nit......even though we have a 30K GBP Agilent spectrum analyser sitting in the workshop, wi-spy is just so convienient.

[Chris Barron]

Thanks for that Lester.
In the end my chosen modules, the ETRX2 by Telegesis turned out to be based on the Ember250 chip.
In normal operation the unit has a function which finds the quietest channel before forming the network. Operating any 2.4GHz equipment while it runs this 1 minute long routine helps it to select the best channel. Obviously , it may be a different story at the other end of the wireless llink.

I think I read somewhere that the replacement for the EM250, known as the EM260, may have the ability to run split channel operation for that reason.

I can't complain about the EM250, the automatic quiet channel function got me out of a problem I had with interference from a badly made video sender. The EM260 would be my first choice these dayd just because they seem even easier to use !


Chris










think I read that the replacemebt

[lester]

Yes, the Telegesis solutions are nice, well engineered products.

Notice though, they promote Wi-Spy on their web site http://www.telegesis.com/telegesis_z...rt_/wi-spy.htm for the very reasons that i mentioned.

There is nothing better than visualising the environment that you are working in, to better understand what your wireless link is 'seeing'.

Rememeber the zigbee prodcuts and wifi products only look at the spectrum on a per channel basis....its what they cannot see thats important!

So its worth remebering that there is a low cost solution for Spectrum analysis should you need it.

I also recall that in Circuit celler there was a 2.4ghz analyser project, so its quite feasable to build one if you are working in that area a lot.

The Circuitcellar hardwrae, PBPro and a 128x64 GLCD make a great portable spectrum analyser with better than per channel resolution.